Good morning.
おはようございます。 Ohayō gozaimasu. (oh-hah-YOH go-zigh-moss) i thought it was pronounced (oh-hah-YOH-go-zigh-mass) why is it moss instead of mass? isn't it with the ah sound not oh sound????

hachiko

you're right in how it's pronounced with the ah sound.
but when you think about it. if you were to say the word moss, it does have the ah sound right.
and when you say mass, it's like your saying the state massachusetts.
i hope that makes sense